We think here are two really good ways to see Joshua Tree in the warmer seasons. BTW, we were there in June with highs of 85 to 100 F, and people told us it was unseasonably cool!
Way 1 is for artists, writers, work-at-homers, exam-preparers, people who want to do a retreat or a small seminar. This is the sort of thing we did, and the nice thing is to rent one of the many vacation rentals in the area for a few weeks, settle down to do your work and go out into the desert in the morning and evening.
Way 2 allows you to get a really good feel of Joshua Tree in a single day, even if it's pretty warm. It involves spending one or two nights around Yucca Valley, walking 4 to 8.5 miles and driving about 170 miles. The ideal thing is to start as early as you can bear, which would mean getting maps and admission fees sorted out the evening before if possible. The National Park Center on Park Boulevard in Joshua Tree opens 8.00 - 5.00. Having seen most of the more accessible parts of Joshua Tree, I think this is the best itinerary for seeing the maximum variety of desert environment, with most of the walking in the cooler morning. You need a lot of water and sunscreen in Joshua Tree. Lots of water means maybe a couple of gallon-size bottles in the car from which you would refill smaller drinking bottles. The water will get hot, but it's better than dehydration.
- Entering the park from West Park Boulevard in Joshua Tree, the pull-offs in the flats are a great place to stop and take a good look at a Joshua Tree Forest.
- The Hidden Valley nature trail (1 mile) is the most beautiful first introduction to this desert park I could imagine.
- The Barker Dam nature trail (1.3 miles) is a great introduction to human use of the desert with its Native American pictographs and the artificial lake behind the dam. Wall Street Mill trail (1.5 miles) from the same car park leads to abandoned cars and mill machinery,. We did have some issues with evening mosquitoes in both these areas. If you really hate walking you could skip one or both of these. Barker Dam is the most interesting walk.
- It requires a detour, but Keys View loop (0.25 miles) has an unmissable panorama to the south with views over the San Andreas fault and Salton Sea. This is the highest altitude on this route and almost certainly as cool as it's likely to get.
- For seeing the higher desert plateau and the boulder piles for which Joshua Tree is famous I think it's enough to do either Skull Rock nature trail (1.7 miles) or the Arch Rock nature trail (0.3 miles). The shade of boulders is a good place to get some respite from the heat.
- There are no more Joshua Trees in the southern lower part of the desert, but there are chollas. The one's on the Cholla Cactus Garden nature trail (0.25 miles) are monstrous. Please, please don't touch the chollas.
- Ocotillos at Ocotillo Patch are another wild and wacky plant. Ocotillo Patch is just a pull-off, not a walk..
- The Cottonwood Spring nature trail (1.4 miles) leads to a botanically beautiful little area that gives the idea of a desert oasis if there isn't time or it's too hot to walk to an official one. It's even possible to drive all the way to the car park overlooking the spring (about 0.25 miles).
- Drive back round to Yucca Valley on Interstate 10 and 52. The wind farm at the intersection of these two roads is strangely monstrous. Route 52 after the intersection is quite attractive.
- In Yucca Valley, turn off down Pioneertown Road for a few miles, for drinks and a meal at Pappy and Harriet's. Check out their music program - most concerts start at 7:30 pm, they cost quite a bit but must be great fun. If you show up for dinner at 7:30 you may find you have to pay for the concert too. We were here at lunchtime so I'm not sure
The most rewarding longer walks we did in Joshua Tree were Ryan Mountain which was challenging because of the heat, but a great view, and 49 Palms Oasis, which was really pretty, but a bit disappointing in that the actual oasis area is protected.